Reaction: Fe2O3 + ascorbic acid
Expected result : Fe (II) complex + H2O
XRD is performed two times, but it gives two different XRD spectra.
Question:
What is the respective product for the two spectra separately?
I think that the two patterns are similar. The pattern 2 is just more scattered. The patterns 1 seems to show preferred orientation effects on some peaks (at about 23.5 and 30°). The phases seem correctly identified by the bars, hematite (with two different pdf card, but similar peaks) and ascorbic acid. Maybe during the collection of the pattern for the second time some instrumental parameter was changed or the sample preparation was less accurate (less sample amount for example)
Mr. Ning,
There is unable quantitative treatment of these data. Could you provide the original files?
Dear Cheung,
the reason you have two different XRD spectra is simply the fact, that between the two recordings a chemical reaction was taking place.
Regarding the chemistry of Ascorbic acid and iron(III) you have to consider the following: Four different types of reaction occur:
1) reduction of Fe(III) to Fe(II).
For instance do the following experiment. Add a drop of FeCl3 solution to ascorbic acid dissolved in water: the yellow colour of Fe(III) imediately vanishs, indication the reduction to colourless Fe(II).
Now, prepare a more alkaline ascorbate solution, add Na2CO3 to ascorbic acid until pH 8, you have basically sodium ascorbate. Adding now a drop of FeCl3, you will obtain a blue-violet solution, an Fe(III)-ascorbate complex. After 5 min the solution turns colourless, you end up with Fe(II). So the reduction rate is strongly pH dependent.
2) complex formation
You already know that transition metals form complexes with ascorbate.
3) aerobic decomposition in the presence of oxygen
Metal ions catalyze the oxidation of ascorbate via oxygen from the air, this means the ascorbate in any metal-ascorbate complex decomposes in the presence of oxygen and moisture. Instead of a single oxidation product there are several pathways and many products.
4) anerobic decomposition of metal ascorbates (in the absence of oxygen)
Even in the absence of oxygen, the metal ions favor a decomposition of the ascorbate ring, leading to a wealth of organic molecules. The more alcaline the pH, the faster occurs the anerobic decomposition.
Have you ever wondered why there are no metal-ascorbate crystal structures reported in the literature?
It is exactly due to the problem of anerobic decomposition, this reaction is faster than the crystallization process. Crystal structures you can find only for "boring" metals such as Na and Ca, but not for the interesting transition metals or the lanthanides.
I hope these comments are helpful for your further research.
If you wish to prepare any new metal-ascorbate complex, I suggest you find a way to work in non-aqueous medium under nitrogen atmosphere.
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